Some troops can deal with the death/killing in a normal manner, while others do f'd up stuff. Regardless of how a troop deals with the psychological trauma, we on the homeland should just say "thank you" and then shut the F up. Anybody that can justify killing by simply telling themself "the U.S gov't told me that this is the bad guy and therefore killing is ok"; worries me a lot more than somebody that struggles with killing and then deals with it by turning off their emotions.
